At present, vacuum devices have been widely used in various industries, including devices for manufacturing various electronic elements in the semiconductor industry, and have become indispensable for the leading scientific technological fields such as high energy physics and solid surface science. For example, with respect to the vacuum devices used for manufacturing semiconductor electronic parts and LSIs, an ultra-high vacuum in a range from 10−5 Pa to 10−7 Pa has been required, and with respect to the ultra-high vacuum film-forming devices used for forming high-quality semiconductor thin-films and ultra-structural films, a pressure in range of not more than 10−8 Pa is required. Moreover, in the next generation high-degree information communication society, there are demands for developing single-electron devices and new electron-optical devices which provide high-speed information communication devices and large-capacity information recording processes, and in order to create these new devices, it is required to control a layer-laminating process in the order of one atom layer under a very clean ultra- to extremely-high vacuum. In other words, in the devices for manufacturing these new devices, there have been strong demands for developing vacuum devices which easily achieve a pressure in a range of not more than 10−8 Pa.
Conventionally, ultra-high vacuum containers and ultra-high vacuum parts are generally made of stainless steel and aluminum alloy, and in such generally-used vacuum devices, in order to achieve an ultra-high vacuum range of not more than 10−5 Pa, an initial evacuation process is carried out for 5 to 8 hours after activation of an evacuation device, and it is necessary to successively carry out a process referred to as a vacuum baking process (vacuum baking) for approximately 5 to several tens of hours. Moreover, in the case of devices which require an ultra- to extremely-high vacuum of not more than 10−8 Pa, for example, vacuum film-forming devices for laminating multiple layers of semiconductors having a film thickness of, for example, several nanometers, it is necessary to combine a plurality of ultra-high vacuum pumps, such as sputter ion pumps and titanium sublimation pumps, and it is also necessary to provide shroud (coolant reservoir) that has been cooled by liquid nitrogen in the device.
Moreover, in general, since stainless steel and aluminum alloy release a large quantity of gases, it is difficult to obtain a pressure of not more than 10−8 Pa by using only an evacuation process, and at present, it is possible to somehow achieve an ultra- to extremely-high vacuum of not more than 10−8 Pa by using specially-cleaned steel in which impurities are reduced in the steel and further finishing the surface thereof to a mirror surface through a polishing process.
As described above, in the conventional generally-used ultra-high vacuum device, an evacuation device using a plurality of ultra-high vacuum pumps combined with one another is required, and in the ultra-high vacuum containers and ultra-high vacuum parts, special steel in which impurities have been reduced is required, and mirror-surface finishing needs to be carried out on the surface thereof, resulting in high costs of the device. Moreover, in order to maintain an ultra-high vacuum, it is necessary to continuously drive the vacuum device, resulting in high driving costs. Furthermore, since it takes a long time to achieve a predetermined ultra-high vacuum, the resulting problem is a reduction in the rate of operation.
In order to solve these problems with vacuum devices, studies and developments, which attempt to practically utilize titanium or titanium alloys that have been seldom used for vacuum devices conventionally because of high costs thereof in comparison with stainless steel and the like so as to easily achieve an ultra- to extremely-high vacuum of not more than 10−8 Pa, have been carried out energetically.
In other words, although expensive in comparison with stainless steel and the like, titanium or titanium alloys have comparatively high strength and light weight, and are superior in corrosion resistance, and since these are produced through a high-vacuum refining process, the quantity of gas mixture into the metallographic structure during the refining process is extremely small, and the resulting material is preferably used as ultra-high vacuum containers, etc.; thus, for example, in accordance with studies made by the inventors, etc. of the present application (T. Chijimatsu, et. al., J. Vac. Soc. Jpn. Vol 42, No. 3, pp200-203 (1999)), it has been clarified that in comparison with stainless steel, titanium has a very small quantity of outgassing, that is, approximately {fraction (1/10)}.
With respect to the technique for applying titanium to the vacuum device, for example, a vacuum device (U.S. Pat. No. 3,030,458) in which metal (preferably titanium) that has been subjected to a high-vacuum refining process, and also has been subjected to a buff polishing process, an electrolytic polishing process and the like so as to have a surface roughness of not more than 100 nm, has been disclosed.
However, titanium has a disadvantage in that it is difficult to carry out a surface smoothing process. In other words, in accordance with the studies by the present inventors, etc., disclosed in the above-mentioned document, the surface roughness of titanium that has been subjected to generally-used buff polishing and electrolytic polishing is approximately 15 nm that is approximately 4 times greater than that of stainless steel that has been subjected to the same polishing processes; therefore, it is difficult to carry out a surface smoothing process to form the vacuum material surface into a mirror surface that is required for supplying an ultra-high vacuum container having a small quantity of outgassing that can achieve an ultra- to extremely-high vacuum of not more than 10−8 Pa in a short time.
Moreover, a metal gasket flange made of titanium, which is used for sealing vacuum, has a problem in that, when a metal gasket made of oxygen free copper, which is normally used in many cases, is applied, vacuum leakage tends to occur even in applications of approximately 10 times.
With respect to titanium alloys, since industrial titanium alloys generally have high strength, and have problems with the mechanical machining properties or surface processability that are required for a material for vacuum devices, material developments have been carried out so as to be applied to vacuum devices, and, for example, an ultra-high vacuum titanium alloy (Japanese Patent Laid-Open Publication No. H06(1994)-065661), which has a small quantity of gas discharge, and contains a platinum based metal, a transition metal, a rear-earth element and the like, and an ultra-high vacuum container (Japanese Patent Laid-Open Publication No. H06(1994)-064600) using such a titanium alloy have been disclosed, and it has been shown that the quantity of outgassing is set to not more than {fraction (1/10)} of that of stainless steel. However, these conventional techniques have disclosed nothing about the surface proccessability, etc. of the material that are required for providing an ultra-high vacuum container capable of providing an ultra- to extremely-high vacuum in a short time, which is the objective of the present invention. Moreover, since comparatively expensive alloy elements are used in these conventional techniques, the resulting devices cause high costs.
Here, with respect to titanium alloys, in addition to the application for vacuum devices, various material developments have been carried out, and, for example, a technique (Japanese Patent Laid-Open Publication No. H10(1998)-017962), which uses iron and oxygen as alloy elements so as to provide a high strength titanium alloy that is superior in the decorative property, toughness, processing property, organism compatibility and cost performance, and is particularly useful as a material for accessories, has been disclosed, and a technique (Japanese Patent Laid-Open Publication No. H10(1998)-017961), which uses iron, oxygen and silicon as alloy elements, has been disclosed to indicate applicability to a wide range of products such as sports products in addition to the application as accessories. However, these conventional techniques have not disclosed anything clearly about the applicability as a material for vacuum devices, such as a outgassing property and a surface processability.
The present invention has been devised to solve the above-mentioned problems with the vacuum device, and its object is to provide a titanium alloy vacuum container and vacuum parts which can achieve an ultra-high vacuum in a short time through evacuation.